In On the Road, we see different kinds of alcohol use, including abuse and alcoholism in Dean’s missing father. Both drug and alcohol use can be sources of money problems and poverty, as characters repeatedly prioritize drugs or alcohol over food and other necessities. Alcohol is one lens through which to view America, both as it exists in the 1940s and as it has changes over time (Bull Lee discusses the decay of America via the loss of "the Ideal Bar"). Alcohol and drugs become a tool through which we can see Dean and Sal’s relationship, as Sal’s dreams and actions when he is high or drunk parallel those of a sober Dean.
Through Dean and Old Bull Lee, Kerouac draws connections between intense drug use and wisdom in On the Road.
The attitude and visions that Sal is able to obtain only with drugs is what Dean experiences all the time. Sal uses drugs to be more like Dean.